Fin end for fin-tube panel



1967 I. BERMAN ETAL 3,303,876

FIN END FOR FIN-TUBE PANEL Filed Sept. 25, 1965 4 Sheets-Sheet l /t/ v E/\/ TUFPS I. EEA /T/mv RD. P 13721,

E M J1 J7 ug/v59 Feb. 14, 1967 1. BERMAN ETAL 3,303,876

FIN END FOR FIN-TUBE PANEL Filed Sept. 23, 1965 v 4 Sheets-Sheet 2 Feb. 14, 1967 BERMAN ET AL FIN END FOR FIN-TUBE PANEL 4 Sheets-Sheet 3 Filed Sept. 23, 1965 w C N 9 5 7 a H 0 M w W m 5 W Q. W p 5 M W W 4 a W V W A W W I m w 3 m M y r N 2 z I W W M J i A y W w w Feb. 14, 1967 i. BERMAN ET AL FIN END FOR FIN-TUBE PANEL 4 Sheets-Sheet 4.

Filed Sept. 25, 1965 QFQ QR" QR United States Patent 3,303,876 FIN END FUR BEN-TUBE PANEL Irwin Barman, New York, N.Y., and Pardhubhai Dahyabhai Patel, Carteret, Ni, assignors to Foster Wheeler ilorporation, Livingston, NJ, a corporation of New York Filed Sept. 23, 1965, Ser. No. 439,605 3 tllainis. (Cl. 165-81) This invention relates to the construction of fin-tube panels and, more particularly, to the construction of the fin ends for fin-tube panels.

In the construction of fin-tube panels, as used for example in steam generators, transverse stresses have been found to concentrate in the ends of the panels. In addition, in the construction of such panels it is essential that they be sealed at the ends. Use of reinforcement members to seal the ends has been found to result in increased transverse stresses.

Therefore, it is an object of this invention to provide a fin of improved construction for use at the fin ends in a fin-tube panel.

Another object of this invention is to provide a fin for use at the fin ends of a tin-tube panel which minimizes transverse stresses at the fin ends of the panel.

Still another object of this invention is to provide a fin for use at the fin ends of a fin-tube panel which seals the fin ends of the panel.

In accordance with this invention, an end fin is provided between two adjoining tubes having a main fin between them. The end fin includes a center section for redistributing transverse stresses to the outer surface of the tubes to eliminate bending along with an inner section to connect the center means to the main fin. An outer section provides a flat sealing surface between the two tubes.

The invention may be better understood from the following detailed description considered in conjunction with the accompanying drawings in which:

FIGURE 1 is a top plan view showing the end fin between two tubes of a fin-tube panel.

FIGURE 2 is a cross-sectional view taken along lines 2 of FIGURE 1.

FIGURE 3 is an isometric view of a portion of a fintube panel incorporating the invention.

FIGURE 4 is a plotted graph showing transverse thermal stresses in a panel using an unimproved fin end.

FIGURE 5 is a plotted graph showing transverse thermal stresses in a fin-tube panel using an improved fin end in accordance with this invention.

Referring now to the drawings, two or more tubes 21 are located side by side with their longitudinal axis parallel and in a common plane. A space is left between the tubes and a main fin 23 is formed within the space between the tubes 21 by any one of a variety of techniques.

An end fin 26, best described as a tapered bend plate or TBP, has an inner section 27, a center section 29, and an outer section 31. The function of the inner sec tion 27 is to connect to the main fin 23 and transfer the transverse end thermal stresses to the center section 29. The function of center section 29 is important, in that it redistributes the transverse end thermal stresses in such a way that it essentially eliminates tube bending. It gradually shifts the transverse end thermal stresses towards the new end. The function of the outer section 31 is to provide a flat sealing surface which is desired at the ends of the welded fin-tube panels used in steam generators. Moreover, due to geometry and the much lower probability of defects in the improved fin end-26, stress concentration may also be reduced. The inner section 27 exice tends from and lies in a common plane with the main fin 23. It should be noted that the inner section 27 is preferably substantially thinner than the main fin 23 having a thickness in the order of approximately one-half the thickness of the main fin 23. The center section 29 lies in a plane at an acute angle With the plane of the inner section 27. As the center section 29 extends away from the inner section 27, it divergse to retain contact with the walls of the tubes 21 which become further removed from one another in planes farther removed from the plane common with their longitudinal axis which is also the plane of the inner section 27. The center section 2% extends from the inner section 27 until it reaches a plane common with the outside surface of the tubes 21. The outer section 31 extends toward or to the ends of the tubes 21 and provides the necessary flat sealing surface. A weld bead 33 secures the end fin to the main fin 23 and the tubes 21.

Previous investigations concerning thermal stresses have shown that where a large metal plate is subjected in one area along its longitudinal axis to a comparatively hot temperature and another area along the longitudinal axis is subjected to a comparatively cold temperature, thermal longitudinal stresses occur in the plate. As these longitudinal stresses die out near ends of the plate at opposite ends of the longitudinal axis, transverse stresses build up and become very concentrated at the plate ends. These transverse stresses are tensile in the hot area of the plate and are compressive on the cold side.

No known prior investigation of such thermal stresses has considered their effect upon a fin-tube panel in which one group of contiguous tubes is comparatively hot while an adjoining group of contiguous tubes is comparatively cold. In such a fin-tube panel longitudinal thermal stresses are set up in the regions away from the ends of the tubes. These longitudinal stresses are usually not critical in themselves but create transverse stresses at the ends of the panel in a manner basically similar to the flat plate previously discussed. In a fin-tube panel, the fins act as a fiat plate in which transverse stresses in the plane of the fins are induced in the vicinity of the panel ends. In the tubes, transverse stresses are also induced in the plane and parallel to the plane of the fins. In addition, because of the distance of many points on the tube from the plane of the fins in which the transverse end stresses occur, large bending stresses are developed. This is a distinguishing feature from the flat plate previously discussed. These thermal bending stresses are important in that they are additive to the direct transverse thermal stresses on the inside surface of the tubes at a point ninety degrees from the fins. Of even more importance, these high transverse stresses are additive in the comparatively hot tubes to the hoop stresses caused by the internal pressure.

In addition to the thermal stress problem, residual longitudinal stresses are induced in the fin-tube panel by its manufacture. These longitudinal stresses caused by manufacturing also result in transverse end stresses and in combination with erection stresses or operating stresses can be destructive. For this reason, in fin-tube panels Where the thermal stress problem may be limited or may not exist, as for example a panel in which the tubes alternate between hot and cold, residual stresses from fabrication still cause transverse end stress concentrations which are suificient to necessitate an improved fin-end construction.

Besides the stress problems which occur at the ends of the panel, it is essential that the fin-tube panel be sealed at the ends. The prior technique of sealing has been either with a welded scalloped bar or a flat bar welded to two-inch strips which were first welded between tubes to the fin and tubes so as to create an essentially fiat surface. In both cases, there is substantial restraint to transverse fiexibility at the ends. However, it has been found that such end reinforcement has adverse effects in that the greater restraint can create higher thermal stress.

Since the end fin is of reduced cross-sectional area, the thermal stress in the fin results in a reduced total force on the tubes. In addition, as the end fin extends nearer the tube ends it applies this force not at the centerpoint of the tubes resulting in bending but at the edge thereby applying the force directly through the tube wall. Although only one side of the tube receives the force, the half thickness of the fin reduces the total force approximately by half. At the same time adequate strength against other forces, such as internal gas pressure in a vapor generator, is obtained.

Referring to FIGURE 4, the points inside the circles represent stresses along the longitudinal centerline of the fin as shown in FIGURE 2. It is shown that very high stresses exist at the fin end and they die out rapidly within a few inches. The points inside the square indicate stresses along the tube centerline at ninety degrees to the fin as shown in FIGURE 2. It will be noted that the fin stresses are compressive and the tube stresses are tensile. This then indicates the tube bending effect. From this, it was conjectured and experimentally verified that the stresses at the inner surface of the same tube centerline are even higher. Points indicated by an asterisk in FIGURE 4, indicates the measured transverse stresses at the inner surface of the same tube centerline. The measured values at the fin end on the inside of the same centerline of the tube were twice as high as those on the outside of the same tube centerline and of an opposite nature. The hoop stresses due to internal fluid pressure are subtractive on the cold side of the panel on the inside of the same centerline of the tube. However, these stresses are additive on the hot side of the panel at the same points.

Referring to FIGURE 5, the points inside the circles represent transverse thermal stresses along the same longitudinal centerline of the end fin 26. It is shown that the stress at the end of the end fin 26 is lower than in an unimproved fin. Similarly points inside the squares represent transverse thermal stresses a-long the same centerline of the tubes 21. From this plot, it is noted that the stresses on the outside surface of a tube 21 and in the fin end 26 is of the same sign near the fin end 26. This indicates that in the improved fin construction there is essentially no bending of the tube 21. Thus, the inside surface of the tube 21 should be stressed about the same or less than the outside surface. The reduced fin thickness compared to the tube thickness reduces the total transverse force and consequently reduces the average stress in the tube. At the same time, adequate strength against other forces, such as internal gas pressure in a steam generator is obtained.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

What is claimed is:

1. A fin-tube panel comprising:

at least two tubes located side by side in a parallel spaced relationship;

a main fin formed between each two adjacent tubes and lying in a plane common with the longitudinal axes of said tubes, said tubes extending beyond the end of said main fin;

a fin end extending from said main fin including a center means for redistributing transverse stresses to the outer surface of the tubes to eliminate bending, an inner means connecting the center means to the main fin to transfer transverse end stresses to the center means, an outer means to provide a flat sealing surface between the two tubes; and

means for securing the fin end of the two adjoining tubes.

2. A fintube panel comprising:

at least two tubes located side by side in a parallel spaced relationship;

a main fin formed between each two adjacent tubes and lying in a plane common with the longitudinal axes of said tubes, said tubes extending beyond the end of said main fin;

a fin end extending from said main fin and including an inner section and a center section and an outer section; said inner section including a fiat plate connected to said main fin and lying in the same plane as said main fin, said center section including a flat plate extending from said inner section and located at an acute angle to said inner section and diverging to retain contact with said two adjoining tubes and extending to the outer surface of said two tubes; said outer section including a flat plate extending from said center section and lying in a plane at the outer surface with its edges in contact with said two adjoining tubes; and

a weld means for securing said fin end to said two adjoining tubes.

3. A fin-tube panel according to claim 2 wherein said fin end has a thickness approximately equal to one-half the thickness of the main fin.

References Cited by the Examiner UNITED STATES PATENTS 1,836,603 12/1931 Ladd 1225 2,808,816 10/1957 Langvand 122-235 FOREIGN PATENTS 975,219 10/1961 Germany. 1,048,594 1/1959 Germany. 1,098,145 l/l96l Germany.

394,233 6/1933 Great Britain.

ROBERT A. OLEARY, Primaiy Examiner.

A. DAVIS, Assistant Examiner. 

1. A FIN-TUBE PANEL COMPRISING: AT LEAST TWO TUBES LOCATED SIDE BY SIDE IN A PARALLEL SPACED RELATIONSHIP; A MAIN FIN FORMED BETWEEN EACH TWO ADJACENT TUBES AND LYING IN A PLANE COMMON WITH THE LONGITUDINAL AXES OF SAID TUBES, SAID TUBES EXTENDING BEYOND THE END OF SAID MAIN FIN; A FIN END EXTENDING FROM SAID MAIN FIN INCLUDING A CENTER MEANS FOR REDISTRIBUTING TRANSVERSE STRESSES TO THE 